Det-Tronics U7602B-P Unitized UV Flame Detector/Controller - Manual (Page 6)

The highest reliability with regard to response to a fire
is achieved when a hazardous area is supervised by
more than one detector, and when each detector can
independently register an alarm.
SYSTEM DESCRIPTION
The U7602 fire detection system consists of a UV
detector module and a controller module housed in a
single explosion-proof enclosure. Both the controller
module, which contains signal processing, automatic
optical integrity and output circuitry, and the UV
detector module, which consists of a UV sensor, UV
test lamp and some signal processing circuitry, are
easily replacable modules. See Figure 1.
DETECTOR
The UV detector portion of the U7602 responds to UV
radiation over the range of 1850 to 2450 angstroms.
It is insensitive to direct or reflected sunlight and to
normal artificial lighting.
In response to UV radiation, the DE1888 detector pro-
duces a series of voltage pulses or “counts.” The fre-
quency of this signal is directly proportional to the
intensity of the radiation being detected and is mea-
sured in counts per second (cps). The cps signal is
sent to the controller portion of the U7602 for process-
ing. If Led indicators are desired, an optional detec-
tor tube module must be specified (i.e. DE1888B).
Automatic Optical Integrity ( oi )
The U7602 is equipped with the Automatic oi feature,
which is illustrated in Figure 2. A UV test lamp is
mounted in the same enclosure with the UV sensor,
but is optically isolated from the sensor by a cylindri-
cal optical shield. When the test lamp is actuated by
a signal from the controller, it generates a UV test sig-
nal (indicated by the dashed line in Figure 2) that
travels out through the viewing window, where it
encounters the reflective snap-in oi ring and is direct-
ed back through the window to the sensor. The con-
troller evaluates the strength of the return signal to
determine the relative condition of the detector and its
optical surfaces. Since this UV test signal must pass
through the same portion of the viewing window as
UV radiation generated by a flame, a reliable test of
the ability of the detector to “see” a fire is achieved.
The U7602 continuously executes the automatic oi
test approximately once per second. If a fault should
occur in the detector/controller, it is quickly detected
and indicated by the Fault Relay contacts opening.
CONTROLLER
The standard U7602 controller module contains two
independent relays and circuitry that produces a cur-
rent output signal. An optional U7602 controller mod-
ule with Form C relays (normally open/normally closed
contacts) and a 4 to 20 ma output is also available.
The controller circuit is contained on five intercon-
nected circuit boards that together make up an easily
replaceable, plug-in controller module (see Figures 3
and 4). The controller module contains a terminal
block (TB3) that allows easy connection to the Fire
and Fault relay contacts and the current output.
When UV radiation received by the U7602 exceeds a
preset sensitivity level for a field adjustable time delay
3 95-8239
CONTROLLER HOUSING
B1501
O-RING
CONTROLLER MODULE
CONDUIT ENTRY
MOUNTING BRACKET
DETECTOR MODULE
O-RING
DETECTOR HOUSING
BULKHEAD
VIEWING WINDOW
oi RING
Figure 1—U7602 Detector/Controller Components